Automatic control of aircraft having pressurized cabins or the like



S p 1958 D. J. LAMBERT ET AL 2,852,213

AUTOMATIC CONTROL OF AIRCRAFT HAVING PRESSURIZED CABINS OR THE LIKEFiled Jan. 9, 1952 3 Sheets-Sheet 3 AUTOMATIC CONTRGL 9F AIRCRAFT HAVINGPRESSURIZED CABENS OR THE LIKE Derek Joseph Lambert and William CharlesGeorge Smith, Weybridge, England, assignors to Vickers-ArmstrongsLimited, London, England Application January 9, 1952, Serial No. 265,664

Claims priority, application Great Britain January 17, 1951 8 Claims.c1. 244-77 This invention relates to aircraft fitted with pressurecabins which may fly at altitudes at which human beings would becomeunconscious due to lack of oxygen if subjected to ambient atmosphericconditions. If a failure of the pressurising system of such an aircraftoccurs, survival of the occupants of the cabin may depend upon a rapidrate of descent to lower altitudes at which breathing of the ambient airwill support life. Below a certain altitude, herein termed the criticalaltitude, the critical forward speed, V at which any aircraft may safelytravel is governed by its structural strength. Above the criticalaltitude, however, compressibility and like effects become ofpredominating importance and the aircraft cannot safely be allowed totravel at a forward speed exceeding a value, V determined by itsaerodynamic behaviour, and it is essential that the aircraft should notbe permitted to fly at a Mach number exceeding a critical valuecharacteristic of the aircraft'in question. At the critical altitude thetwo critical speeds V and V are equal.

The invention aims to provide a system of automatic control which will,without assistance from the pilot, be brought into operation, if thepressurising system fails at a dangerous altitude, to cause the aircraftto dive at a substantially constant Mach number not exceeding thecritical value to an altitude at or approximating to the criticalaltitude and thereafter to continue its dive at a substantially constantequivalent airspeed not exceeding the critical value until a safealtitude is reached, i. e. an altitude at which respiration sufiicientfor recovery from an unconscious state is possible, and then to returnthe aircraft to straight and level flight. In this condition, the pilotmay recover from any temporary incapacity due to lack of oxygen, andwill be able to take over control of the aircraft once more.

The invention accordingly provides an aircraft having a pressure cabinand an automatic pilot, and comprising pressure sensitive means exposedto the pressure within the pressure cabin, normally inefiectivemechanism arranged to be operated automatically by the pressuresensitive means, in response to reduction, at an altitude above thecritical altitude, of the pressure in the pressure cabin to a givenlimit, to control the automatic pilot so as to maintain the aircraf inflight at a substanially constant Mach number not exceeding the criticalMach number, means operative automatically, when the aircraft hasdescended to an altitude at or near to the critical altitude, to modifythe action of said mechanism so that thereafter the aircraft ismaintained in flight at a substantially constant equivalent airspeed notexceeding the critical equivalent airspeed, and means operativeautomatically when the aircraft has descended to a safe altitude toremove the control of said mechanism from the automatic pilot.

In the preferred form of the invention we employ a single electricalMach meter including two pressure sensitive devices, viz. a speedresponsive device exposed to dynamic air pressure and an altituderesponsive device extates Patent Q l posed to atmospheric pressure, apotentiometer system, wipers operated by said pressure sensitive devicesand coacting above the critical altitude with the potentiometer systemto apply to the elevator control of the automatic pilot, when themechanism is in operation, a dive signal representative of the Machnumber, a stop for arresting further movement of the altitude responsivepressure sensitive device when the aircraft has descended to an altitudeat or near to the critical altitude so that the dive signal thereafterapplied to said elevator control is representative of the equivalentairspeed, and a switch which is operative automatically, should the Machnumber or the equivalent airspeed as the case may be reach the criticalvalue, to apply a temporary climb signal to said elevator control.

One specific embodiment of the invention will now be described indetail, by way of example, with reference to the accompanying drawings,in which:

Fig. 1 is a series of graphs illustrating the conditions under which theaircraft will descend from a dangerous altitude in the event of failureof the pressurising systern,

Fig. 2 is a diagram showing an aircraft fitted with the automaticcontrol system according to the invention,

Fig. 3 is a vertical section through a pressure switch,

Figs. 4- and 4A collectively constitute a circuit diagram showing partof a conventional automatic pilot and, within the frame in the diagram,an electrical Mach meter control, and

Figure 5 is an elevation, partly in section, of the electrical Machmeter.

Like reference numerals indicate like parts throughout the figures.

In Fig. 1, the dash lines A indicate lines of constant Mach number M, Mbeing the ratio Aircraft true air speed at a givenaltitude Speed ofsound at that altitude The full lines B indicate lines of constantequivalent airspeed (E. A. S.), the equivalent airspeed being defined bythe formula E. A. S.=True airspeedXV; where air density at a givenaltitude air density at sea level Any given aircraft cannot safely fly,at high altitude, above a certain critical Mach number M. Nor, at alower altitude, can that aircraft safely fly at an E. A. S. exceeding acertain critical value. The invention will be explained hereinafter onthe assumption that it is applied to an aircraft having a critical Machnumber of 0.85, indicated by the line V in Fig. 1, and a critical E. A.S. of 350 knots, indicated by a line V in Fig. 1. The critical altitudefor this aircraft will therefore be 24,000 feet in the InternationalStandard Atmosphere represented by the point C of intersection of thelines V and V If the pressurising system is assumed to fail at analtitude of 50,000 feet, the path of most rapid descent to a safealtitude of 18,000 feet will be represented by the line DCE. Theautomatic control system to be described later is accordingly soarranged that the aircraft will, in such a descent, descend at a speed Vrepresenting a Mach number of 0.85, from 50,000 feet to the criticalaltitude, and will thereafter descend at an E. A. S. of 350 knots fromthe critical altitude to the safe altitude.

The aircraft shown in Fig. 2 comprises a pressure cabin -10, containinga seat 11 for the pilot and an automatic pilot 12 of known constructionoperative, through a servo-motor 13 and a connection 14, on the elevator15. Al'socontained within the pressure cabin is a. control unit '16.This contains the whole of the mechanism contained within the framework17, Figs. 4 and 4A, theloss of pressure switch shown in Fig. 3, theelectrical Mach meter shown in Fig. 5 and a normal pressure switch NPS(Fig. 4), similar to the switch shown in Fig. 3 but arranged, whenactuated, to close contact NPS and opencontact NPS (Fig. 4) as laterdescribed.

The pressure switch LP (Fig. 3), comprises a casing 25, a micro-switch26 and a capsule 27. So long as adequate-pressure is maintained in thepressure cabin, the capsule 27 is maintained away from the micro-switch26. On failureof the pressurising system at high altitude, however, thecapsule 27 will expand, causing a member 28 at the base of the capsuleto depress the plunger '29 of themicroswitch, so completing a circuitbetween leads 130. The normal pressure switch NPS (Fig. 4) is similar tothe switch LP but is arranged to actuate twocontacts NPS NPS (Fig. 4).When the aircraft has descended to a safe altitude, under control of theautomatic control system as later described, the air pressure willcollapse the capsule stack (corresponding to 27) of the normal pressureswitch sufiiciently to close contacts NPS and open contact NPS as laterdescribed. Figs. 4, 4A and 5 illustrate a system of control embodying anovel form of electrical Mach meter. This system is applied to theautomatic pilot 12 which is of the rate/ rate type, i. e. one in which,when under normal pilots control, the rate of application of a dive orclimb signal to the elevator control is determined by the amount ofmovement applied by the pilots control member. Such an automatic pilotis described in British Patent No. 611,037. The electrical Mach meter isin control of the automatic pilot 12 during the whole of the descent toa safealtitude, the altitude responsive portion of the meter beingdisabled below the critical altitude so that the signals given by theinstrument are thereafter representative of E. A. S.

The electrical Mach meter is shown, in circuit'forrn, in the frame 17 inFigs. 4 and 4A, from'which certain parts of the conventional automaticpilot 12 unnecessary for the understanding of the invention have beenomitted. Athree phase supply is connected, via a transformer 58(Fig.4A), to lines 59, 60, 61. .The line 61 is connected to thereference control winding RP of the two phase pitch motor PM of theautomatic pilot, and the windings 59, 60 are alternatively connectable,either by the pilots controller potentiometer PCP or by the Mach meterpotentiometer MMP,'to the control winding C of the pitch motor. Thepitch motor PM is effective to rotate, through gearing 30 and about itspitch axis 31, a tilting platform 32 carrying a gyroscope 33 which, inturn, controls the elevator through the servo mechanism 13, as explainedin British Patent No. 611,037 so as to maintain the aircraft flying atan attitude determined by the pitch motor PM. I

Normally the elevator control servo motor '13 of the automatic pilotwill maintain the aircraft in level'flight. The pilot, however, byactuating a switch (Figs. 2 and 4A) can energize a relay PCR, byconnecting the same through line 40 to a positive supply line 78, toclose contacts. PCRl and PCR2, thereby connecting the potentiomcter PCPto the supply lines 59, 60. His elevator control 21 (Fig. 2) isconnected to a wiper 62 and, by moving this wiper on to the left handsection of the potentiometer PCP he can connect the winding C to thepair of stacks of capsules 63, 64 disposed respectively in housings '65,66. The interior of the housing 65 is subject to dynamic. air pressurethrough a Pitot connection 67, so that the capsule stack 63 isresponsive to airspeed. The interior of the housing 66 is subjectthrough an inlet 166 to atmospheric pressure, so that the capsule stack64 is responsiveto altitude. The capsule stack 63 is connected, by arod-68 to a transmitter, comprising two resistances 69; 69A (Fig. 4A)and a step switch having wipers 70, 70A, disposed. in the upper portion71 of 'the housing 65. The capsule stack 64 is connected, by a rod 72,to a similar transmitter located in the upper portion 73 of thehousing66 and comprising two resistances 74, 74A (Fig. 4A) and a step switchhaving wipers 75, 75A. The altitude responsive capsule stack 64 containsa stop 76 which is adjustable by means of a screw threaded portion 77thereof. When the aircraft has descended to a given altitude, furthercollapse of the capsule stack 64 is prevented by the stop 76.

Returinin'g'to Fig. 4, reduction of the pressure inthe cabin toan-unsafe level while the aircraft is 'ata dangerous altitude causes theabove-described pressure switch LP to close a contact LP1. Thiscompletes a circuit from the'line 7-8, which is connected to a positivesource of supply when the automatic pilot is switched on, to earththrough a loss of pressure relay LPR. This then actuates five'contacts.Closure of contact LPRl prepares a holdin'g circuit'for the relay LPRwhich will'be effective to maintain the relay LPR energized in theevontof contact L'Pi reopening. Opening of contact LPRZ de-ener- .gizesa relay ML, thereby releasing a magnetic latch ML (Fig. 4A) for acontact LS2 of a level flight switch. Normally the magnetic latch ML;holds the contact LS closed as shown in Fig. 4A but when the latch ML isreleased the contact LS is free to open. Closure of contact LBR3energizes a change over relay COR. Closure of contact LPRS energises arelay TA, thereby causing an actuator 44 to move engine throttlecontrols 45 in throttle closing direction to a predetermined position.Closure of contact LPR7 energises a master relay MR, through a controlswitch CS which is spring loaded to the closed position by a spring 34.

The change over relay COR actuates four contacts. Closure of contactCORl establishes a holding circuit for the relay COR. Closure of contactCOR3 (Fig. 4A) connects the Mach meter potentiometer MMP to the controlwinding 'C of the pitch motor PM, via a normally closed contact SR2connected to the dive section of the potentiometer. Closure of contactCORS (Fig. 4) energises a relay DBA to cause an actuator 42 to renderoperative dive brakes 43 or other drag producing mecha- 'nism. Closureof contact COR7 (Fig. 4A) connectsa mercury level switch MJS to thewinding C of'the pitch motor through the contact LS2 when the contactLS2 is closed. This connection replaces the normal connection throughthe contact ECR4 which has now opened. The drawing shows the automaticpilot disengaged, but contact ECR4 is open whenever the automatic pilotis engaged.

The switches LS1 and LS2 are of the mercury level type, 'andLSl makescontact at say 1 of dive-and LS2 at say 1 of climb. The mercury levelswitch MIS will not make contact until say 2 of climb or dive. Whenflying level both contacts LS1 and LS2 will be open. The mercury levelswitch M18 is only brought into normal use when the automatic pilot isfirst engaged. A delay ofso'me 30 seconds ensues before full control ofthe servo motor 13 is obtained and the pitch motor PM would be unstableduring this period. The aircraft is accordingly kept level during thisperiod by the switch M] S after which contact ECR4 opens and normalcontrol is applied via potentiometer PCP and switch MR4.

The'rnaster relay MR (Fig. 4) actuates 5 contacts. Closureof contact MR1establishes a holding circuit for the relay MR. Op'eningofanother-contact MR (Fig.

4A) cuts out of circuit pilot-operated relay PCR for closing thecontacts PCRl and PCR2 and so prevents the pilot from engaging hispilcts controller potentiometer PCP. Closing of contact MR3 (Fig. 4)establishes the above mentioned holding circuit for the relay LPRthrough the normally closed contact NPSZ and the contact LPRl which hasclosed as already described. Opening of contact MR4 (Fig. 4A)disconnects the pitch motor PM from the pilots controller potentiometerPCP. Closure of contacts MR5 and MR7 supplies power to the Mach meterpotentiometer MMP.

The aircraft is now under control of the Mach meter. A dive signal isapplied from the left hand wiper 75 of the potentiometer MMP, throughthe normally closed signal relay contact SR2 to the winding C of thepitch motor PM. The resistances 69, 69A and 74, 74A are so arranged thatthe potential of the left hand Wiper 75 varies inversely with the Machnumber, with the result that the rate at which the dive signal isapplied will be slower the higher the Mach number. In response to thedive signal, the platform of the gyroscope of the pitch motor PM istilted into a position such that the elevator is set appropriately for adive. When the dive commences, the level flight switch closes contactLS1.

The speed responsive capsule stack 63 actuates a further wiper 79 whichmoves over a set of contacts 80 and the altitude responsive capsulestack 64 actuates a similar further Wiper 81 moving over a set ofcontacts 82. Each of the contacts 80 represents a definite range of E.A. S. and each of the contacts 82 represents a definite range ofaltitude. So long as either of the wipers 79, 81 occupies a spacebetween adjoining contacts of the associated bank, the aircraftcontinues to dive at increasing Mach number. At a predetermined Machnumber, however, which is determined by the width and spacing of thecontacts 80, 82, which are suited to the design of the aircraft, bothwipers 79, 81 will make contact with one of their associated contacts80, 82. This results in energization of a relay VS to close a switch VS1(Fig. 4). A circuit is then completed to energise a signal relay SR,thereby opening contacts SR2 and closing contact SR1 (Fig. 4A). Thisremoves the dive signal from the pitch motor PM and substitutes a climbsignal derived from the right hand section of the potentiometer MMP.This reverses the pitch motor PM and sets the elevator to lessen thedive. As soon as one of the wipers 79, 81 leaves its respective switch,the contact VS1 will open again, and the signal relay SR will changeover its contacts SR1, SR2 to the position shown in Fig. 4A and againapply the dive signal. The aircraft will thus dive at a Mach numberapproximating the critical Mach number.

When the aircraft reaches the critical altitude, the stop 76 (Fig. 5)becomes effective, and the wiper 81 (Fig. 4A) remains on the appropriatecontact 82. The Mach meter thenceforth operates as an E. A. S. metercontrolling the dive through the switch VSl so that the aircraftthereafter dives at an E. A. S. approximating to the critical E. A. S.

The dive continues until the aircraft has reacheda safe altitude. Thenormal pressure switch NPS then closes contact NPSI and opens contactNPSZ. Opening of contact NPSZ de-energises the relay LPR, and closure ofcontact NPS}. operates the signal relay SR. This reverses the positionof the contacts SR1, SR2 and applies a climb signal to the pitch motorPM. This signal continues until the level flight switch opens thecontact LS1, to removethe climb signal, and closes the contact LS2,which is then held closed by the magnetic latch ML, which is now able tolock the contact LS in the closed position; since contact LPRZ has nowclosed and re-energized the relay ML. The pitch motor PM is now in thelevel flight position and thenceforth is monitored by the mercury levelswitch MJS, through contacts LS2 and COR7, to keep the aircraft instraight and level flight.

When the pilot desires to restore control to the pilots controllerpotentiometer PCP, he can do so by opening the switch CS, therebydeenergising the relays COR and MR and closing the contact MR in thecircuit for operating the contacts PCRI and PCR2.

The advantages of governing the rate of descent as described above maybe summarised as follows:

(a) Diving, during the first stage, at the critical Mach number ensuresthe minimum possible delay, consistent with safety in reaching a safealtitude, is more rapid than rates of descent governed by permittedconstant airspeed or constant permitted aircraft attitude, and ensuresthat maximum advantage may be taken of the extra drag associated withcompressibility effects.

(b) No previous knowledge of the change of elevator trim with height andspeed are required as the automatic pilot will cater for theseautomatically. This disposes of the disadvantages of a device whichpre-sets the elevator controls to what is believed to be a suitableposition, but which, due to the nature of the compressibility eflectsand possible damage from enemy action, is not in fact correct.

What we claim as our invention and desire to secure by Letters Patentis:

1. In an aircraft, including an elevator, a pressure cabin, an automaticpilot, and an operative connection between the automatic pilot and theelevator, the combination with said automatic pilot of a pressuresensitive device exposed to the pressure within the pressure cabin,normally ineffective dive controlling means operable on said automaticpilot to maintain the aircraft in diving flight at a substantiallyconstant Mach number, means actuable by said pressure sensitive device,on failure of pressure in said cabin above a critical altitude, forplacing the automatic pilot under control of said dive controlling meansfor actuation thereby, means operating automatically, when the aircrafthas descended to an altitude near said critical altitude, to render saiddive controlling means thereafter effective to constrain the automaticpilot to maintain the aircraft in diving flight at a substantiallyconstant equivalent airspeed, and means responsive to further descent ofthe aircraft to a predetermined altitude for disconnecting said divecontrolling means from said automatic pilot.

2. In an aircraft, a combination as claimed in claim 1, comprisingnormally ineffective drag producing means, and means actuable by thepressure sensitive device, on failure of pressure in the cabin above thecritical altitude, to render said drag producing means effective.

3. In an aircraft, a combination as claimed in claim 1, comprising anengine throttle control and means actuable by the pressure sensitivedevice, on failure of pressure in the cabin above the critical altitude,to move said engine throttle control in throttle closing direction.

4. In an aircraft, including an elevator, a pressure cabin, an automaticpilot, and an operative connection between the automatic pilot and theelevator, the combination with said automatic pilot of a pressuresensitive device exposed to the pressure within the pressure cabin, anormally ineffective electrical Mach meter having two sections andoperable on said automatic pilot to maintain the aircraft in divingflight at a substantially constant Mach number, one section of said Machmeter being responsive to equivalent air speed and the other section ofsaid Mach meter being responsive to altitude means actuable by saidpressure sensitive device, on failure of pressure in said cabin above acritical altitude, for placing the automatic pilot under control of bothsections of said Mach meter for actuation thereby, means operatingautomatically, when the aircraft has descended to an altitude near saidcritical altitude, to disable said altitude responsive section of saidMach meter thereby enabling the other section of said Mach meter toconstrain the automatic pilot to maintain the aircraft in diving flightat a substantially constant equivalent air-speed, and means responsiveto further descent of the aircraft to a predetermined altitude'beiowsaid critical altitude forzdisconnecting said Mach meter from saidautomatic pilot.

5."In an aircraft, including an elevator, a pressure cabin, 'anautomatic pilot, and an operative connection between the automatic pilotand the elevator, the combination with said automatic'pilot of apressure sensitive device exposed to the pressure within the pressurecabin, a first potentiometer normally connected to the automatic pilotand manually operable to apply dive and climb signalsto the automaticpilot; a'second potentiometer, normally inoperative connections betweensaid second potentiometer and said automaticpilot for applying diveand*climb signals to the automatic pilot when operative, an electricalrelay system, a switch operable by said pressure sensitive device onfailure of pressure in said cabin above a critical altitude to causesaid relay system to disconnect the first potentiometer from theautomatic pilot and to render operative the dive signal transmittingconnection between the second potentiometer and-the automatic pilot, aMach meter for periodically'rendering said climb signal transmittingconnection operative in place of said dive signal transmittingconnection and thereby maintaining the aircraft in diving flight at asubstantially constant Mach number, said Mach meter comprising sectionsresponsive respectively to equivalent-air speed and to altitude meansresponsive to descent of the aircraft toan altitude near the criticalaltitude for disabling the altitude responsive section of said Mach:meter rendering said meter responsive to airspeed instead of to Machnumber, said meter thereafter controlling the alternative establishmentof said connectionstosmaintain the aircraft in diving flight at asubstantially constant equivalentairspeed, and means responsive tofurther descent of the aircraft to a predetermined altitude below: saidcritical altitude for causing said relay system to disconnect theautomaticpilot from the secondpotentiometer.

6. In an aircraft, including an elevator, .aipressure cabin, anautomatic pilot, and an operative connection between the automatic pilotand the elevator, the combination with said automatic pilot of a,pressure sensitive device exposed to the pressure within thepressurecabin, a first potentiometer normally connected to the "automatic pilotand manually operable to apply dive and climb signals to the automaticpilot, a secondpotentiometer, normally inoperative connections betweensaid second potentiometer and said automatic pilot forv applying diveand climb signals to the automatic pilot when operative, an electricalrelay system, a switch operable by said pressure sensitive device onfailure of pressure in said cabin above a critical altitude to causesaid relay system to disconnect the first potentiometerfromitheautomatic, pilot and-to render operative the dive signaltransmitting connection between the second potentiometer and theautomatic pilot, a Mach meter for periodically rendering said climbsignal transmitting connection operative in place of said dive signaltransmitting connectionand thereby maintaining the aircraft in divingflight .at a substantially constant Mach number, said Mach metercomprising sections responsive respectively toequivalent air speed andtoaltitude means responsive to descent of the aircraft to an altitudenear the critical altitude for disabling the altitude responsive sectionof the Mach meter and thereby rendering said Mach meter responsive toairspeed instead of to Mach number, said means thereafter controllingthe alternative establishment of said connections to maintain theaircraft in vdiving flight at a substantially constant equivalentairspeed, a second pressurevsensitive device, a switch operable therebyon further descent ofthe aircraft to a predetermined sa'fe altitudetoestablish the climb signal transmitting connection between the secondpotentiometer and the automatic pilot, a level flight switch mechanismfor rendering said climb signal transmitting connection inoperative whenthe aircrafthas attained level flight, and a further level flightswitch'for thereafter monitoring the automatic pilot to maintain theaircraft in level flight.

7. In :an aircraft, including an elevator, a pressure cabin,an:automatic pilot, and an operative connection between the automaticpilot and the elevator, the combination with-said automatic pilot of apressure sensitive member exposed to thepressure within'the pressurecabin, a normally ineffective electrical Mach meter, comprising a firstpressure sensitive device exposed to dynamic air pressure, a secondpressure sensitive device exposed to atmospheric pressure, apotentiometer system including sections for. respectively applying adivesignal-and a climb signal to vthe automatic pilot, and wipersactuated by said first a-ndsecond pressure sensitive devices andrespectively cooperating with the dive and climb sections ofthepotentiorneter system, means actuable by said pressure sensitivemember, on failure-of pressure in the cabin above a critical altitude,to-connect to said automatic pilot the wipercoacting with the divesection of .the potentiometer system, thereby causing the aircraft todive, .a switch, switch actuating means controlled by said first andsecond pressure sensitive devices for periodically actuating said switchto connect to the autopilot the wiper coacting with the climb section ofthe potentiometer sysem in placeof the wiper coacting with the divesection .ofthe potentiometer system, thereby maintaining the aircraft indiving .fiight at a substantially constant Machnumber, a stop forarresting further movement of said second pressure sensitive device whenthe aircraft has descended to an altitude near the critical altitude andthereby modifying the action of said switch controlling means,said-switch controlling means thereaftermaintaining theaircraft indiving flight at a substantially constant equivalent airspeed, and meansresponsive to further descent of the aircraft to a predeterminedaltitudebelow said critical altitude for disconnecting said potentiometer systemfrom said automatic pilot.

8. -In an aircraft, a combination-as claimed in claim 7, wherein saidswitch controlling means comprises a first step switch actuated by thefirst pressure sensitivedevice and havingcontacts each of which isrepresentative of a definite range of equivalent airspeed, a second stepswitch actuated by the second pressure sensitive device and havingcontacts each of which is representative of a definite range ofaltitude, and a relay operative, so long only as I contacts aresimultaneouly made by both step switches,vto

cause said'switch to connect to the automatic pilot the wiper associaedwith the climb section of the potentlometer.

- References Cited in the file of this patent "UNITED STATES PATENTSGreat Britain July 11, 1951 All

